Nanoscale Photodetector Could Advance, Miniaturize Optoelectronics

MADISON, Wis. and BUFFALO, N.Y., July 10, 2017 — Using a high-yield, high-throughput fabrication method, nanometer-thin photodetectors with enhanced light absorption have been demonstrated. The photodetectors, which are based on a nanocavity interference mechanism, could enable miniaturization of optoelectronic devices, leading to performance gain without adding bulk.

The research addressed two remaining challenges to the thinning of photoactive layers to the nanometer scale: how to prevent incomplete photon absorption and low quantum efficiency due to weak light-matter interaction and how to maintain single-crystalline quality in the ultrathin material.

The device was developed by researchers at the University of Wisconsin-Madison (UW-Madison) and the University at Buffalo (UB). It consists of nanocavities sandwiched between a top layer of ultrathin single-crystal germanium and a reflecting layer of silver. The nanocavity structures used for the device have been shown, in previous work by the researchers, to increase the amount of light that thin semiconducting materials, e.g. germanium, can absorb.

Shrinking photodetectors like this one, created and tested in the laboratory of UW-Madison engineering Professor Zhenqiang (Jack) Ma, help make consumer electronics smaller. Courtesy of Stephanie Precourt/UW-Madison.“Because of the nanocavities, the photons are ‘recycled’ so light absorption is substantially increased — even in very thin layers of material,” said UW-Madison professor Zhenqiang (Jack) Ma.

To manage the quality of the germanium thin films, researchers used a novel membrane-transfer technology that allowed them to integrate single crystalline semiconducting materials onto a substrate. This resulted in a very thin, yet effective, light-absorbing photo detector for smaller optoelectronics applications.

“It is an enabling technology that allows you to look at a wide variety of optoelectronics that can go to even smaller footprints, smaller sizes,” said professor Zongfu Yu of UW-Madison, who conducted computational analysis of the detectors.

While the advance was demonstrated using a germanium semiconductor, the researchers believe that their method could be applied to other semiconductors.

“And importantly, by tuning the nanocavity, we can control what wavelength we actually absorb,” said professor Qiaoqiang Gan from UB. “This will open the way to develop lots of different optoelectronic devices.”

UW-Madison electrical and computer engineering graduate student Zhenyang Xia holds a dish containing photodetector samples. The sample colors vary depending on how they are tuned to absorb a specific light wavelength. Courtesy of Stephanie Precourt/UW-Madison.Smaller optoelectronic devices could be used to reduce the size and weight of solar panels and to speed data transmission.

The researchers are applying jointly for a patent on the technology through the Wisconsin Alumni Research Foundation.

A sub-field of photonics that pertains to an electronic device that responds to optical power, emits or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electrical-to-optical or optical-to-electrical transducer. Electro-optic often is used erroneously as a synonym.